Loudspeaker assembly and system

ABSTRACT

A loudspeaker assembly is disclosed for use in a loudspeaker system having infinite baffle topology. The assembly comprises a driver including a cone and a basket and at least one Helmholtz resonator including a chamber and a vent duct communicating with the chamber and adapted to pass through the infinite baffle. The chamber is dimensioned to provide a tuned frequency well above an operating band associated with the driver. The cross sectional area and length of the vent duct may be set to provide control over duct air noise and low frequency extension. A method of tuning a loudspeaker assembly for use in a loudspeaker system having infinite baffle topology is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 USC §371 ofInternational Application No. PCT/AU2010/001405, filed Oct. 22, 2010,which claims the benefit of and priority to Australian PatentApplication No. 2009905165, filed Oct. 23, 2009, the entire disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a loudspeaker assembly suitable for usein a loudspeaker system. The assembly is particularly suited toloudspeaker systems having infinite baffle topology operating below 300Hz and in particular to systems that include a Helmholtz resonator.

BACKGROUND OF THE INVENTION

Helmholtz resonators are added to loudspeakers for three main reasons:

(i) to provide extension at low frequency by tuning at or near a bottomend of an operating band associated with a loudspeaker driver;

(ii) to provide acoustic filtering by tuning at or near a top end of theoperating band; and

(iii) to create cone minima in the operating or pass band.

In each case the physical form of the resonator is easily recognizableas a chamber containing a volume of air and a vent duct. The presentinvention may make use of a Helmholtz resonator for an entirelydifferent reason and in a form that may be distinctly different toHelmholtz resonators of the prior art.

The present invention is suited to a loudspeaker system having infinitebaffle topology. Although the term “infinite” is used to describebaffles they are not literally infinite, but rather are very large ineffect. For example the walls, ceiling or floor of a room, or the roof,walls or floor of a vehicle may be regarded as infinite baffles forpractical purposes.

One potential problem associated with application of infinite baffletopology to loudspeakers in vehicles is structural weakening. Forexample cutting large holes, such as for a 12 inch loudspeaker driver inany part of a vehicle may cause structural weakening.

One known way around this problem is to mount the loudspeaker driver ina separate box and to channel sound to a listening environment through amuch smaller opening.

There are several known ways of doing this. One way is via suitablydesigned waveguides. Another way is to use a vent duct associated with aHelmholtz resonator to penetrate a rear parcel shelf or deck of avehicle to channel the sound to the listening environment.

Known Helmholtz resonators used to penetrate parcel shelves in vehiclesare tuned in traditional ways to create band pass alignments and/or toextend low frequency response and/or to create cone minima in the passband as described above. When used in these ways prior art infinitebaffle topology loudspeaker systems using Helmholtz resonators areinherently large. Infinite baffle topology loudspeakers withoutHelmholtz resonators roll off at a low end of their operating band witha similar cut off frequency to sealed box topology loudspeakers. Thisarrangement cannot provide low frequency extension.

The present invention may provide a loudspeaker assembly comprising anelectro-acoustic transducer or driver and at least one Helmholtzresonator suitable for use in a loudspeaker system. The loudspeakerassembly may be relatively small in size and may have a relatively highsensitivity. It may also have a relatively very low cut off frequencycompared to sealed box topology for a same or similar driver.

Prior art teaches that low frequency extension is achieved by tuninglow, near the desired low frequency cut off. It is counter intuitive inprior art that low frequency extension could be achieved by tuninghigher, above the operating band of the loudspeaker assembly.

Tuning higher to provide low frequency extension would have an advantagethat the loudspeaker assembly may be very small. The loudspeaker may bemade as small as desired to satisfy practical requirements includingcost and space availability. In some applications it may be appropriateto make the loudspeaker assembly even smaller to achieve a desiredresponse.

Reactive components of a loudspeaker system comprising a driver mountedin a baffle may be modelled as a parallel resonant circuit. Reactivecomponents of a Helmholtz resonator may be modelled as a series resonantcircuit. When a Helmholtz resonator is added to a loudspeaker drivermounted in a baffle the components of the series resonant circuitinteract with the components of the parallel resonant circuit toproduce:

-   -   a) a lower tuned frequency which determines a low frequency roll        off commonly called the “low cut off frequency”;    -   b) an intermediate tuned frequency commonly called the “box        tuning” or “port tuning”; and    -   c) an upper tuned frequency which determines a high frequency        roll off.

For avoidance of doubt a reference to a frequency well above anoperating band is a reference to the upper tuned frequency.

A reference herein to a patent document or other matter which is givenas prior art is not to be taken as an admission that that document ormatter was, in Australia, known or that the information it contains waspart of the common general knowledge as at the priority date of any ofthe claims.

Throughout the description and claims of this specification, the word“comprise” and variations of the word, such as “comprising” andcomprises”, is not intended to exclude other additives or components orintegers.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided aloudspeaker assembly suitable for use in a loudspeaker system havinginfinite baffle topology, said assembly comprising a driver including acone and a basket and at least one Helmholtz resonator including achamber and a vent duct communicating with said chamber and adapted topass through said infinite baffle, wherein said chamber is dimensionedto provide a tuned frequency well above an operating band associatedwith said driver.

The volume of the chamber may be dimensioned so that it is relativelycompact or miniature relative to a chamber that is dimensioned toprovide a tuned frequency within or close to the operating bandassociated with the driver. For example a 20 cm driver may be associatedwith a Helmholtz resonator including a chamber volume that may bebetween marginally above zero volume to substantially 3 liters.

The cross sectional area of the vent duct may be set to minimize airnoise in the vent duct and length of the vent duct may be set to controllow frequency extension.

The loudspeaker assembly may include two Helmholtz resonators whereinone resonator is positioned on each side of the driver.

In some embodiments the assembly may be adapted for use in a motorvehicle. The infinite baffle may include a perimeter of a passengercompartment of the vehicle and the duct may be adapted to pass throughthe perimeter. The infinite baffle may include an outer skin of thevehicle and the duct may be adapted to pass through the outer skin. Theduct may be adapted to pass through an existing opening in the skin suchas a ventilation port.

The frequency response of an associated loudspeaker system may be rolledoff at or near a top end of the operating band by means other than aHelmholtz resonator.

In a limiting case the chamber of at least one Helmholtz resonator mayapproach zero volume except for air trapped in an excursion range orswept volume associated with the cone.

The present invention may provide a composite loudspeaker assemblyincluding at least one loudspeaker assembly as described above whereinthe composite assembly is arranged such that it is acousticallysymmetrical. The composite assembly may include two substantiallyidentical loudspeaker assemblies arranged face to face and adapted to bedriven as an isobaric pair.

According to a further aspect of the present invention there is provideda loudspeaker assembly suitable for use in a loudspeaker system havinginfinite baffle topology, said assembly comprising a driver including acone and a basket wherein said basket includes a substantiallycontinuous barrier to trap air behind said cone in a rear chamber formedby said barrier and said cone, said rear chamber being vented by a ventduct in said basket.

The loudspeaker assembly may include a further barrier for trapping airin front of the cone in a front chamber formed by the further barrierand the cone. The front chamber may be vented by a further vent duct inthe further barrier.

The present invention may provide a composite loudspeaker assemblyincluding two loudspeaker assemblies arranged face to face with a sealedspace there between, wherein each loudspeaker assembly is constructedwith air trapped in a rear chamber as described above and is adapted tooperate as an isobaric pair.

According to a further aspect of the present invention there is provideda loudspeaker assembly suitable for use in a loudspeaker system havinginfinite baffle topology, said assembly comprising a driver including acone and a basket wherein said driver includes a substantiallycontinuous barrier for trapping air in front of said cone in a frontchamber formed by said barrier and said cone, said front chamber beingvented by a vent duct in said continuous barrier.

The present invention may provide a composite loudspeaker assemblyincluding two loudspeaker assemblies arranged back to back, wherein eachloudspeaker assembly is constructed as described above and the compositeassembly is adapted to operate as an isobaric pair.

According to a further aspect of the present invention there is provideda method of tuning a loudspeaker assembly for use in a loudspeakersystem having infinite baffle topology, said assembly including a driverhaving a cone and a basket, and at least one Helmholtz resonator havinga chamber and a vent duct communicating with said chamber and adapted topass through said infinite baffle, said method comprising dimensioningsaid chamber to provide a tuned frequency well above an operating bandassociated with said driver.

The method may include setting cross sectional area of the vent duct tominimize air noise in the vent duct and setting length of the vent ductto control low frequency extension.

A loudspeaker assembly according to the present invention may befabricated from prior art components. Alternatively it may bemanufactured in a form of a driver with one or more inbuilt Helmholtzresonators.

The present invention may allow a loudspeaker assembly to be installedin an infinite baffle regardless of noise, dust, mud, water and/or otherenvironmental conditions including on a side of a baffle opposite alistening environment by orienting an aperture of a vent to that side ofthe baffle. Shielding from noise, dust and the like may be provided asrequired.

DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings wherein:

FIG. 1 shows a schematic representation of a typical prior art infinitebaffle topology loudspeaker system without a Helmholtz resonator;

FIG. 2 shows a schematic representation of a typical prior art infinitebaffle topology loudspeaker system incorporating a Helmholtz resonatorwith tuning at a high end of an operating band;

FIG. 3 shows a schematic representation of an infinite baffle topologyloudspeaker system using a single Helmholtz resonator according to oneembodiment of the present invention;

FIG. 4 shows a schematic representation of an infinite baffle topologyloudspeaker system using a single Helmholtz resonator according to analternative embodiment of the present invention;

FIG. 5 shows a schematic representation of an infinite baffle topologyloudspeaker system using two Helmholtz resonators situated in a vehicleaccording to an embodiment of the present invention;

FIG. 6 shows a typical prior art loudspeaker driver;

FIG. 7 shows a loudspeaker assembly with a Helmholtz resonator on a rearside thereof according to an embodiment of the present invention;

FIG. 8 shows a loudspeaker assembly with a Helmholtz resonator on afront thereof according to an embodiment of the present invention;

FIG. 9 shows a loudspeaker assembly with Helmholtz resonators on bothsides thereof according to an embodiment of the present invention;

FIG. 10 shows a composite loudspeaker assembly with Helmholtz resonatorson both sides thereof according to an embodiment of the presentinvention;

FIG. 11 shows a composite loudspeaker assembly with Helmholtz resonatorson both sides thereof according to an embodiment of the presentinvention;

FIG. 12 shows a mechanically balanced composite loudspeaker assemblywith Helmholtz resonators on both sides and a Helmholtz resonator in thecentre thereof according to an embodiment of the present invention; and

FIG. 13 shows a cross section of a loudspeaker assembly with front andrear Helmholtz chambers in which volumes associated with the Helmholtzchambers are approaching zero.

DETAILED DESCRIPTION OF THE INVENTION

A known method of constructing an infinite baffle topology loudspeakersystem is simply to mount a loudspeaker driver directly to an infinitebaffle as shown in FIG. 1. In FIG. 1 loudspeaker driver 10 is mounted toinfinite baffle 12 and radiates sound to a listening environment 15.FIG. 1 also shows a frequency response graph including a roll off ateach end of an operating band associated with driver 10. Roll off at thehigh end may be achieved by electrical means. Low frequency roll off isa consequence of driver parameters. Driver 10 in FIG. 1 is shown facingforwards towards the listening environment 15. This is a common priorart arrangement because it does not project into the listeningenvironment 15. A disadvantage of this particular topology is that theresponse cannot be adjusted for low frequency extension.

One known means of adjustment is to add a Helmholtz resonator. A typicalprior art infinite baffle topology loudspeaker with a Helmholtzresonator is shown in FIG. 2. In FIG. 2 chamber 20 in combination withvent duct 21 are mounted to infinite baffle 22 to form the Helmholtzresonator.

Loudspeaker driver 23 is mounted in chamber 20 containing air volume 24and is vented via vent duct 21 to listening environment 25. Vent duct 21penetrates infinite baffle 22 which has an advantage in that only asmall hole is required in baffle 22.

Prior art Helmholtz resonators as shown in FIG. 2 are typically tuned toroll off at f_(H), being at the high end of the operating bandassociated with driver 23, as shown on the frequency response graph inFIG. 2 to create an acoustic band-pass structure. Chamber 20 istypically much larger than driver 23. Note that the operating band inthe graph in FIG. 2 is defined by a roll off at each end.

FIG. 3 shows loudspeaker driver 30 mounted to infinite baffle 31. InFIG. 3 chamber 32 is formed by cone 33 of driver 30 enclosing small airvolume 34 between itself and front wall 35. Chamber 32 is vented by ventduct 36 which passes through infinite baffle 31 and radiates sound tolistening environment 37. Chamber 32 and vent duct 36 form a Helmholtzresonator. Also shown in FIG. 3 is an associated frequency responsegraph showing roll off at both ends of the operating band associatedwith driver 30 with the Helmholtz resonator tuned high to produce a rolloff at f_(H) being well above the operating band.

Tuning of the Helmholtz resonator to produce a roll off well above theoperating band is achieved by making chamber 32 substantially smallerthan prior art Helmholtz chambers used in infinite baffle topologyloudspeakers for low frequency applications. Chamber 32 may typically besimilar in size to driver 30. In the example of FIG. 3 chamber 32 issmaller in volume than driver 30. In practical applications chamber 32may range from zero volume up to several times the volume of driver 30so long as the Helmholtz resonator is tuned to produce a roll off wellabove the operating band.

It is preferable to orientate the loudspeaker system such that vent duct36 radiates sound to listening environment 37 as shown in FIG. 3.However it is also possible to reverse the orientation as shown in FIG.4. The elements shown in FIG. 4 are similar to FIG. 3 although theprefix 3 designating each element is changed to a 4. For example baffle31 in FIG. 3 becomes baffle 41 in FIG. 4. In FIG. 4 driver 40 radiatessound to the listening environment 47 from the back of the cone. Howeverthis is not a preferred embodiment for most applications in part becausethe response of such an arrangement is far from ideal.

FIG. 5 shows a practical arrangement of an infinite baffle topologyloudspeaker system situated in a wall of a vehicle including outer skin51 and lining 52. Loudspeaker driver 53 is enhanced with (a) a frontHelmholtz resonator including small air volume chamber 54 resonatingwith vent duct 55 to provide tuning well above the operating band ofdriver 53 and (b) a rear Helmholtz resonator including small air volumechamber 56 resonating with vent duct 57 to provide tuning also wellabove the operating band of driver 53.

The relatively small Helmholtz resonator chambers 54, 56 enable theloudspeaker system to be placed in locations that may be impractical forinfinite baffle topology loudspeakers using prior art Helmholtzresonator alignments. In FIG. 5, vent duct 55 is shown penetrating outerskin 51 of the vehicle via ventilation port 58, while vent duct 57penetrates vehicle lining 52 to radiate sound to a listening environment59 inside the vehicle.

Manufacturers may find value in being able to use existing openings inthe skin of a vehicle. Alternatively if there are no existing openingsin desired locations additional openings may be provided. In a preferredembodiment a vent duct may penetrate the outer skin of a vehicle, butperformance may be traded for cost saving by penetrating a rear parcelshelf, deck or fire wall of the vehicle.

In other examples the infinite baffle topology loudspeaker of thepresent invention may be installed in a wall, ceiling, roof or floor ofa building.

FIG. 6 shows a prior art loudspeaker driver 60 comprising a magnet 61, abasket 62, vent holes 63 in basket 62 allowing air to flow through inresponse to cone movement, and a small volume of air 64 between basket62 and the cone of driver 60.

Since the volume of air required for a Helmholtz resonator according tothe present invention may be relatively small, a loudspeaker assembly 70as shown in FIG. 7 may be constructed wherein vent holes 63 as seen inFIG. 6 are not provided. Instead basket 71 is enclosed except for a ventduct 72. The volume between basket 71 and the cone of assembly 70 form aHelmholtz resonator together with vent duct 72.

Alternatively a loudspeaker driver 80 including basket 81 may beenclosed at the front as shown in FIG. 8 by wall 82 forming a smallcavity vented by vent duct 83 to create a loudspeaker assembly accordingto the present invention.

In each example the Helmholtz resonator may result in a high frequencyroll off well above the intended operating band of the driver 70, 80 dueto the small enclosed air volumes. The cross sectional area of theassociated vent ducts 72, 83 may be varied to minimize duct air noiseand the length of the vent ducts may be varied to set a desired lowfrequency extension.

FIG. 9 shows an enhanced version of a loudspeaker assembly for use ininfinite baffle topology applications according to the presentinvention. Driver 90 in FIG. 9 includes a Helmholtz resonator on eachside of driver 90. Basket 91 of driver 90 is enclosed except for ventduct 93 and the front of driver 90 is enclosed by wall 92 except forvent duct 94. In a preferred embodiment the Helmholtz resonators soformed may produce a high frequency resonance at the same frequencywhich is well above the intended operating band of driver 90.

FIG. 10 shows a symmetrical version of a composite loudspeaker assemblyaccording to the present invention wherein the composite assembly isformed from two loudspeaker assemblies arranged face to face so thattheir cones trap a volume of air between them. Each loudspeaker assemblyhas its respective basket 102 and 103 enclosed except for vent ducts 104and 105. Motor assemblies 100 and 101 of the loudspeaker assemblies maytypically be wired out of phase so that their cones move in the samedirection. The cavity between the cones forms a dead volume thatoperates as an isobaric chamber.

FIG. 11 shows an alternative symmetrical version of a compositeloudspeaker assembly according to the present invention wherein twoloudspeaker assemblies are arranged back to back with magnets 110 and111 facing each other and potentially butting together. The fronts ofloudspeaker assemblies 110,111 are enclosed by respective walls 112 and113 except for vent ducts 114 and 115. Associated baskets 116, 117 andmotor assemblies are housed in a cylindrical enclosure 118 shown cutaway in FIG. 11. The associated motor assemblies may be wired out ofphase so that cylindrical enclosure 118 operates as an isobaric chamber.

FIG. 12 shows a further enhancement of a composite loudspeaker assemblyaccording to the present invention wherein two loudspeaker assemblies120, 121 are arranged face to face and are joined by cylindricalenclosure 122. The baskets 123, 124 of loudspeaker assemblies 120, 121are enclosed except for vent ducts 125, 126 to form Helmholtzresonators. Cylindrical enclosure 122 joining loudspeaker assemblies120, 121 is vented by vent duct 127 to a listening environment and formsa third Helmholtz resonator.

In the above example motor assemblies associated with loudspeakerassemblies 120, 121 may typically be wired in phase (not isobaric) toprovide mechanically balanced operation with minimal vibration. EachHelmholtz resonator may be tuned to produce a resonant frequency that iswell above the intended operating band of the composite loudspeakerassembly. In a preferred embodiment each Helmholtz resonator may betuned to produce the same resonant frequency.

In some embodiments according to the present invention there may belittle or no value in giving any volume to the chambers of the Helmholtzresonators. The volume may be substantially zero other than allowing forcone excursion or as close to zero as is practical. FIG. 13 shows how a“zero volume” loudspeaker assembly 130 may be constructed according tothe present invention. In FIG. 13, cone 131 separates rear Helmholtzresonator chamber 132 from front Helmholtz resonator chamber 133.Chambers 132, 133 are vented by vent ducts 134 and 135 respectively. Itmay be seen that after allowing for cone excursion remaining enclosedair volumes associated with chambers 132, 133 are very small or close tozero.

Finally it is to be understood that various alterations, modificationsand/or additions may be introduced into the constructions andarrangements of parts previously described without departing from thespirit or ambit of the invention.

The invention claimed is:
 1. A loudspeaker assembly forming part of aloudspeaker system having an infinite baffle, said assembly comprising:a driver including a cone and a basket; and at least one Helmholtzresonator including a chamber and a vent duct communicating with saidchamber and adapted to pass through said infinite baffle, wherein saidchamber is formed by said cone with air trapped therein with said ventpassing through the infinite baffle, wherein said chamber is arranged totune air trapped between said cone and the infinite baffle, and whereinsaid chamber is dimensioned to provide a tuned frequency well above anoperating band associated with said driver.
 2. The loudspeaker assemblyaccording to claim 1, wherein volume of said chamber is miniaturerelative to a chamber that is dimensioned to provide a tuned frequencywithin or close to said operating band associated with said driver. 3.The loudspeaker assembly according to claim 1, wherein cross sectionalarea of said vent duct is set to minimize air noise in said vent duct.4. The loudspeaker assembly according to claim 1, wherein length of saidvent duct is set to control low frequency extension.
 5. The loudspeakerassembly according to claim 1, including two Helmholtz resonatorswherein one resonator is positioned on each side of said driver.
 6. Theloudspeaker assembly according to claim 1 adapted for use in a motorvehicle, wherein said infinite baffle includes a perimeter of apassenger compartment of said vehicle and said vent duct is adapted topass through said perimeter.
 7. The loudspeaker assembly according toclaim 6, wherein said infinite baffle includes an outer skin of saidvehicle and said duct is adapted to pass through said outer skin.
 8. Theloudspeaker assembly according to claim 7, wherein said duct is adaptedto pass through an existing opening in said skin such as a ventilationport.
 9. The loudspeaker assembly according to claim 1, whereinfrequency response of said loudspeaker system is rolled off at or near atop end of said operating band by means other than a Helmholtzresonator.
 10. The loudspeaker assembly according to claim 1, whereinthe chamber of at least one Helmholtz resonator approaches zero volumeexcept for air trapped in an excursion range associated with said cone.11. A loudspeaker system including a loudspeaker assembly according toclaim
 1. 12. The loudspeaker assembly of claim 1, wherein said basketincludes a substantially continuous barrier and said resonator includesa rear chamber formed by said barrier and said cone to trap air behindsaid cone, said vent duct communicating with said rear chamber via saidbasket.
 13. The loudspeaker assembly of claim 12, further comprising asecond barrier for trapping air in front of said cone in a front chamberformed by said second barrier and said cone, said front chamber beingvented by a second vent duct in said second barrier.
 14. The loudspeakerassembly of claim 1, wherein the chamber of at least one Helmholtzresonator approaches zero volume except for air trapped in an excursionrange associated with said cone.
 15. The loudspeaker assembly of claim1, wherein said driver includes a substantially continuous barrier andsaid resonator includes a front chamber formed by said barrier and saidcone for trapping air in front of said cone, said vent ductcommunicating with said front chamber via said continuous barrier.
 16. Amethod of tuning a loudspeaker assembly forming part of a loudspeakersystem having an infinite baffle, said assembly including a driverhaving a cone and a basket, and at least one Helmholtz resonator havinga chamber and a vent duct communicating with said chamber and adapted topass through said infinite baffle, said method comprising: forming saidchamber by said cone with air trapped therein, said chamber beingarranged to tune air trapped between said cone and said infinite baffle,the vent duct passing through the infinite baffle, and dimensioning saidchamber to provide a tuned frequency well above an operating bandassociated with said driver.
 17. The method of tuning a loudspeakerassembly according to claim 16, wherein volume of said chamber isminiature relative to a chamber that is dimensioned to provide a tunedfrequency within or close to said operating band associated with saiddriver.
 18. The method of tuning a loudspeaker assembly according toclaim 16, including setting cross sectional area of said vent duct tominimize air noise in said vent duct.
 19. The method of tuning aloudspeaker assembly according to claim 16, including setting length ofsaid vent duct to control low frequency extension.